1. Field of the Invention
The present invention relates to a magnetic disk for use in a magnetic recording/regenerating device.
2. Description of the Prior Art
Prior practice commonly employs random accessible disk-shaped magnetic disks as memory means in computers, etc. Substrates of such magnetic disks generally include those of aluminum alloy, glass or plastic, etc., practically the aluminum alloy substrates chiefly.
For the aluminum alloy substrate, there is applied a base curing processing such as Ni-P plating or an anodized aluminum processing and the like. Thereafter, for finishing a disk surface into a mirror surface polishing is carried out, and for forming protrusions, on the disk surface a texturing processing is carried out. The texturing enjoys its advantage to reduce the attraction of any foreign matter by the magnetic disk and provide magnetic anisotropy to a magnetic film of the magnetic disk circumferentially. Such a magnetic disk includes on a substrate rendered to the texturing a magnetic film layer, a protective film layer, and a lubricating film layer laminated successively, which disk can be manufactured manifesting excellent characteristics: electromagnetic conversion characteristic, lifting characteristic, contact-start-stop characteristic, and attraction characteristic.
The magnetic disk drive generally employs a contact-start-stop system in which three states: rest (contact), slide, and floating are existent between a magnetic head and a magnetic disk. More specifically, the magnetic head makes contact with the magnetic disk and rests on the same when the magnetic disk is stationary, and the magnetic head and the magnetic disk make contact with each other and slide during the lower speed rotation of the magnetic disk, and further the magnetic head floats on the magnetic disk without contact, spaced away by 0.2 to 0.5 .mu.m from the surface of the latter during stationary rotation of the magnetic disk. In the contact-start-stop system, however, it repeats the contact, slide, and floating between the magnetic head and the magnetic disk, and hence frictional characteristics between the magnetic head and the magnetic disk are increased and results in the so-called head crush where the magnetic disk or the magnetic head is broken down. To solve this, measures are taken in which a magnetic disk surface is coated with a solid lubricant or a liquid lubricant for example. There might thereupon occur a strong attraction phenomenon between the magnetic disk and the magnetic head owing to application of such a lubricant on the magnetic disk, however. The attraction phenomenon might present strong load onto the magnetic head and a flexure as a supporter for the magnetic head upon the magnetic disk drive being started in its operation to cause a damage on the magnetic head and the flexure or cause a severe scratching damage on the surface of the magnetic disk. Texturing is therefore needed to slightly apply a lubricant on the magnetic disk to the degree where there are produced no friction and wear even though the contact, start, and stop are repeated.
Prior practice of such texturing employs a polishing tape in which a lubricant is fixed and retained on a tape. The texturing can be performed by pressing a polishing tape against a magnetic disk substrate while rotating the substrate. Hereby, a texture line has protrusions with the maximum surface roughness R.sub.max of 0.02 to 0.1 .mu.m, and is directed coaxially circumferentially in the running direction of the magnetic head (as disclosed in Japanese Patent Laid-Open No. 61-51619) or alternately directed in a direction deviated by 3 or more degrees of rotational angle from the circumferential direction (as disclosed in Japanese Patent Laid-Open No. 2-73516). These texturing processings are to form texture lines of one kind on the disk substrate.
Requirement is accumulated recently of increasing the capacity of recording of the magnetic disk drive device. Some methods are proposed to satisfy the need: 1) Thickness of a magnetic film layer of the magnetic disk is made thinner; 2) Coercive force Hc of a magnetic film layer of the magnetic disk is increased; 3) A gap length of the magnetic head is reduced; and 4) The degree of floating of the magnetic head is reduced; and so on. For this, the degree of floating of the magnetic head is gradually being decreased from 0.2 .mu.m to 0.1 .mu.m.
Such prior practice however suffers from difficulties that when a contact-start-stop test is performed with the lower degree of floating of the magnetic head of 0.1 .mu.m, the sliding time and sliding distance of the magnetic head are increased to result in the wear of a magnetic disk surface and hence a change in the surface configuration of the magnetic disk and further that wear powder produced on the magnetic disk adheres to the magnetic head to result in head crushing.
Referring to FIG. 13, there are illustrated changes in the coefficients .mu. of dynamic friction in the contact-start-stop testing in a prior art magnetic disk as the degree of floating of the magnetic head is changed. As illustrated in the same figure, it is understood that the coefficient .mu. of dynamic friction steeply rises as the degree of floating of the magnetic head is reduced, to result in deterioration of the contact-start-stop characteristic.
Furthermore, there is disclosed in Japanese Patent Laid-Open No. 3-125325 another technique to form on a substrate of a magnetic disk textures intersecting in an angular range of from 0.1 to 20.0 degree, but with description only of the contact-start-stop characteristic and with no description of any improvement of the attraction characteristic as well as the floating characteristics.